Hundreds of web firms are tracking every single keystroke made by visitors, a study from Princeton University has suggested.The technique - known as session replay - is used by companies to gain an understanding of how customers use websites.

These scripts record your keystrokes, mouse movements, and scrolling behaviour, along with the entire contents of the pages you visit, and send them to third-party servers," the researchers said in a blog.

"Collection of page content by third-party replay scripts may cause sensitive information such as medical conditions, credit card details and other personal information displayed on a page to leak to the third party as part of the recording.

Firms using the software included the UK's news website the Telegraph, Samsung, Reuters, US retail giant Home Depot and CBS News.

Theres no excuse for this sort of activity, I have visited some of these sites and will now not ever do so again, I hope many of you will do the same and let such entities know spying on visitors is immoral, unethical and most probably illegal.